In the past, the technique of detecting spatial information such as a distance to an object existing in a target space by receiving light from the target space, into which an intensity modulated light is being projected, and determining a phase difference in the modulation component between the projected light and the received light has been known. For example, as introduced in PCT International Publications Nos. WO96/15626 and WO2004/008175A, a spatial information detection device based on this technique is basically formed with a light emitting source for projecting a light intensity-modulated with a predetermined modulation period into the target space, a photodetector having a photoelectric converting portion configured to receive light from the target space, and generate electric charges corresponding to a received light amount, and an evaluation portion configured to detect the spatial information of the target space from a change between the light projected from the light emitting source and the light received by the photodetector.
By the way, since this kind of detection device projects the intensity-modulated light into the target space, there is an inconvenience when detecting the spatial information from a common target space by a plurality of detection devices. That is, when plural lights are simultaneously projected into the target space from the detection devices, it becomes difficult to distinguish the light projected from the light emitting source of one of the detection devices into the target space from the light projected from another one of the detection devices into the target space. In other words, each of the detection devices cannot extract only the light projected into the target space by its own light emitting source from the plural lights projected into the target space. As a result, it leads to a deterioration in detection accuracy of the spatial information.